In a manufacturing process of a semiconductor device, in some cases, a process of oxidizing a surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) that is a substrate is performed.
Meanwhile, an ALD (Atomic Layer Deposition) method is known as the process in which the oxidation is performed. In some cases, a process of forming a thin film such as silicon oxide (SiO2) on a surface of a wafer using the ALD method is performed. In a film forming apparatus for performing the ALD method, a mounting unit of a wafer is installed in a processing vessel (vacuum vessel) of which the interior is set to a vacuum atmosphere. Then, the supply of a source gas containing a source of silicon to the mounted wafer and the oxidation of the source adsorbed onto the wafer are alternately repeated a plurality of times.
The oxidation of the source has been performed by supplying an oxidation gas such as oxygen or ozone to the substrate, by supplying hydrogen and oxygen to the substrate to generate oxygen radicals, or by generating plasma by oxygen in a vacuum vessel. However, when the oxidation gas is supplied, it is necessary to heat the wafer at a relatively high temperature in order to allow the oxidation gas to chemically react with the source. When the oxygen radicals are generated, it is also necessary to heat the wafer at a relatively high temperature in order to generate the radicals. When the oxygen plasma is used, although components of the source gas deposited on the wafer can be oxidized even at room temperature, there is a difference in film quality between a planar portion and a side portion of a pattern of the wafer due to the straight-ability of plasma active species consisting of ions or electrons. Thus, the film quality of the side portion is degraded as compared with that of the planar portion. For this reason, the adaptation to a fine pattern is difficult.
Therefore, a heating mechanism such as a heater is conventionally installed in a film forming apparatus. However, the heating mechanism installation as described above increases the manufacturing cost or operating cost of the apparatus, and the oxidation of the source cannot be performed until the wafer is loaded into a vacuum vessel and then heated to reach a predetermined temperature. Hence, it is difficult to promote reduction in processing time. However, in the related art, a technique applied to the above-described ALD method is not described. Also, in the related art, oxygen gas, nitrogen gas and hydrogen gas are supplied and mixed in a reduced pressure atmosphere to generate reactive species (atomic oxygen). However, since in order to generate the atomic oxygen, the temperature of an atmosphere where each gas is supplied becomes 400 degrees C. to 1200 degrees C. by the heater, the above-described problem cannot be solved.